The present invention is in the field of circuit boards; more particularly, the invention relates to an improved circuit board made of a cross-linked polycyanurate polymer, thermoplastic polymer, and polyaramid fiber.
As indicated in D. C. Packard, "KEVLAR.RTM. Epoxy Substrate for Interconnecting Leadless Chip Carrier", SAMPE Journal, Vol. 20, No. 1, pp. 6-14 (January/February 1984), experimental circuit boards for interconnecting leadless chip carriers are disclosed to be made from composites of epoxy and polyaramid fibers (Kevlar).
Printed circuit board technology is well established for producing leaded insertion electronic component printed wiring assemblies. More recently, printed circuit boards have been developed for leadless chip carriers. Leadless chip carriers are well known in the art. An integrated circuit chip is carried by the leadless chip carrier. The combination of the chip and the carrier are interconnected to form proper circuits. U.S. Pat. No. 4,444,309 discloses a carrier for a leadless integrated circuit chip.
The development of the leadless chip carriers has enabled printed circuit boards to have much higher component densities. The package can now have electrical connections on all sides of the chip carrier and there is the elimination of space required to component leads.
In the past, in microcircuit applications used flat packs or dual in line packages. The differential thermal expansion between the microcircuit package and the board/substrate was accommodated by flexibility in the device leads. The microcircuit package was of a ceramic material such as aluminia having a coefficient of thermal expansion of +6.4.times.10.sup.-6 cm/cm/.degree.C. The flexibility to compensate for differential thermal expansion with the use of leadless chip carriers is not there since the device is soldered directly to the substrate material. As indicated in the referenced article by Packard, even minor differences in the coefficient of expansion of the substrate and the leadless chip carrier can result in micro-cracking in the resin of the fiber resin substrate composite.